Experiments on the effects of guanidine (and guanidine derivatives) on transmitter release from frog motor nerve terminals will be conducted. Nerve terminals blocked by TTX will be exposed to various concentrations of guanidine and the effect on miniature end-plate potential frequency assessed. Experiments on the effect of axotomy on the synaptic input to lamprey reticulospinal neurones will be conducted. Lamprey Muller axons will be cut in the spinal cord and intracellular recordings made from the cell bodies in the brain. The effect of axotomy on the ultrastructure of lamprey cell bodies and axons will be determined. In other experiments the relationship of activity in Muller axons to movements in intact lampreys will investigated. Extracellular recording from Muller axons will be correlated with various kinds of spontaneous and evoked trunk movements.